In a gas turbine engine, air is pressurized in a compressor, then mixed with fuel and burned in a combustor to generate hot combustion gases. The hot combustion gases are expanded within the turbine section where energy is extracted to power the compressor and to produce useful work, such as turning a generator to produce electricity. The hot combustion gas, also called the working gas, travels through a series of turbine stages that are numbered starting at 1 from front to back of the turbine section. A turbine stage includes a circular array of rotating turbine blades, and may also include a circular array of stationary vanes. The blades extract energy from the working gas for powering the compressor and providing output power. Commonly, each blade is removably mounted on the circumference of a disk.
A turbine blade has a tip that closely clears a surrounding shroud. The shroud channels the working gas through the turbine section. The inner lining of the shroud is made abradable so the blade tips can cut a path in it to minimize the tip-to-shroud clearance, and minimize leakage of the working gas from the pressure side to the suction side of each blade. Some blade designs include a tip shroud as shown in FIG. 1. The shroud is a transverse plate on the blade tip. A seal rail may extend radially outward from the shroud. The term “radial” herein means along a radius from the turbine rotation axis. The rail is aligned circumferentially with the rotation direction. It cuts a narrow groove in the shroud lining for working gas sealing. The rail may include wider portions called teeth that cut the groove wider than the rail to minimize friction. Cantilevered portions of the tip shroud must be rigid to resist flexing from centrifugal force.